This phenomena (was) is known as diplacusis. Almost 40% of population have
it. I'm not able to find oldest source, but Bekesy (Experiments in Hearing,
McGraw-Hill, 1960, page 601) is talking about: "... the "diplacusis"
between two finger tips ...is much larger than the diplacusis found in
normal ears.". The basic idea why and how it happen is also explained.
In German Journal "Hoergeräete Akustik" (now. "Audiologische Akustik") in
early 70-thies a paper was published explaining that this phenomena have to
do with non-musical hearing. It is wrong, while I have difference of almost
one semi tone, and am able to tune for example a guitar without any
reference hearing only left or right (and not pushing a strings to have
equal tones). I do not hear any replay (interference) if listening
binaurally, and both my thresholds are almost the same. Loudness dependent
pitch shift was described in JASA (Snow, Vol. 8 (!!), No 1 ) and still
actual but not having anything with diplacusis.
Zlatan Ribic
Dr. Ribic GmbH
A. Baumgartnerstr. 44
1230 Vienna
Austria